<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no" name="viewport" />
    <meta content="yes" name="apple-mobile-web-app-capable">
    <title>canvas</title>
    <style>
        body{
            padding:0;
            margin:0;
        }
        canvas{
            background:#eee;
            padding:0;
        }
        div{
            color: #000;
            background: #ddd;
            font-size: 16px;
        }
         p{
            position: absolute;
            left:420px; top: 50px;
            padding: 10px 30px;
            color: white;
            font-size: 20px;
            font-family: "Microsoft Yahei";
            
        }
        #canvas{
            cursor: pointer;
            background:#000;
        }
    </style>
</head>
<body>
    <canvas id="canvas"></canvas>
    <script src='../js/ball.js'></script>
    <script src="../js/arrow.js"></script>
    <script src='../js/utils.js'></script>
    <script>
        window.onload = function(){
            var canvas = document.getElementById("canvas");
            var context = canvas.getContext('2d');
            canvas.width = document.body.clientWidth;
            canvas.height = window.screen.availHeight*0.8;

            
          var    balls = [],
          numBalls = 100,
          bounce = -1;

      for (var ball, i = 0; i < numBalls; i++) {
        ball = new Ball(Math.random() * 15 + 1, Math.random() * 0xffffff);
        ball.x = Math.random() * canvas.width ;
        ball.y = Math.random() * canvas.height;
        ball.vx = Math.random() * 6 -3;
        ball.vy = Math.random() * 6 -3;
        balls.push(ball);
      }

     //collision
      function checkCollision (ballA, i) {
        for (var ballB, j = i + 1; j < numBalls; j++) {
          ballB = balls[j];
          dx = ballB.x - ballA.x;
          dy = ballB.y - ballA.y;
          dist = Math.sqrt(dx * dx + dy * dy);
          min_dist = ballA.radius + ballB.radius;

          if (dist < min_dist) {    
            ballA.vx *= bounce;
            ballA.vy *= bounce;
            ballB.vx *= bounce;
            ballB.vy *= bounce;
          }
        }
      }
        
      //边界检测
      function move (ball) {
       
        ball.x += ball.vx;
        ball.y += ball.vy;
          
        if (ball.x + ball.radius > canvas.width) {
          ball.x = canvas.width - ball.radius;
          ball.vx *= bounce;
        } else if (ball.x - ball.radius < 0) {
          ball.x = ball.radius;
          ball.vx *= bounce;
        }
        if (ball.y + ball.radius > canvas.height) {
          ball.y = canvas.height - ball.radius;
          ball.vy *= bounce;
        } else if (ball.y - ball.radius < 0) {
          ball.y = ball.radius;
          ball.vy *= bounce;
        }
      }

      //draw
      function draw (ball) {
        ball.draw(context);
      }

      (function drawFrame () {
        window.requestAnimationFrame(drawFrame, canvas);
        context.clearRect(0, 0, canvas.width, canvas.height);

        balls.forEach(checkCollision);
        balls.forEach(move);
        balls.forEach(draw);
      }());
    

        }
    </script>
</body>
</html>
